Auto ISO is a pretty simple idea. The camera increases the ISO by just enough in low light to maintain a 'safe' shutter speed. And if the light improves, it drops the ISO again. It's a great way to make sure that you always get a shake-free exposure while increasing the ISO by as little as possible.
I first started using it during my years on N-Photo magazine. Nikon's DSLRs always did Auto ISO rather well, with an 'Auto' setting for the minimum safe shutter speed with the option to make this automatic shutter speed 'slower' for expert hand-holders or 'faster' for hopeless hand-holders like me.
Honestly, you should try it. Auto ISO is just a brilliant way to guard against slow shutter speeds and blur when shooting handheld. Obviously you'll switch it off for tripod shots and long exposures, but the rest of the time it does nothing when it's not needed and might just save your shot when it is.
But I've realized Auto ISO is not quite as smart as I thought it was. And on some cameras it's not very smart at all.
